Jerusalem: The United States and Britain have monitored secret sorties and communications by Israel`s air force in a hacking operation dating back to 1998, according to documents attributed to leaks by former U.S. spy agency contractor Edward Snowden.

Israel voiced disappointment at the disclosures, published on Friday in at least two media outlets and which might further strains ties with Washington after years of feuding over strategies on Iran and the Palestinians.

Israel`s best-selling newspaper, Yedioth Ahronoth, said the US National Security Agency, which specialises in electronic surveillance, and its British counterpart GCHQ spied on Israeli air force missions against Gaza, Syria and Iran.

The spy operation, codenamed "Anarchist", was run out of a Cyprus base and targeted other Middle East states too, Yedioth said.

Online publication The Intercept, which lists Snowden confidant Glenn Greenwald among its associates, ran a similar report, with what it said were hacked pictures of armed Israeli drones taken from cameras aboard the aircraft.Yedioth said German news-magazine Der Spiegel, whose publication day is Saturday, also planned to run an article based on Snowden`s leak.

Israel neither confirms nor denies having armed drones, though one of its senior military officers was quoted as acknowledging them in a secret U.S. diplomatic cable from 2010 that was published by Wikileaks.